1. Field of the Invention
This invention generally relates to wireless communications antennas and, more particularly, to a multi-frequency recursive pattern antenna and a method for forming the same.
2. Description of the Related Art
As noted in U.S. Pat. No. 6,140,975 (Cohen), antenna design has historically been dominated by Euclidean geometry. In such designs, the closed antenna area is directly proportional to the antenna perimeter. For example, if one doubles the length of an Euclidean square (or “quad”) antenna, the enclosed area of the antenna quadruples. Classical antenna design has dealt with planes, circles, triangles, squares, ellipses, rectangles, hemispheres, paraboloids, and the like. Similarly, resonators, typically capacitors coupled in series and/or parallel with inductors, traditionally are implemented with Euclidian inductors. The prior art design philosophy has been to pick a Euclidean geometric construction, e.g., a quad, and to explore its radiation characteristics, especially with emphasis on frequency resonance and power patterns. The unfortunate result is that antenna design has far too long concentrated on the ease of antenna construction, rather than on the underlying electro-magnetics.
One non-Euclidian geometry is fractal geometry. Fractal geometry may be grouped into random fractals, which are also termed chaotic or Brownian fractals and include a random noise components, or deterministic fractals. In deterministic fractal geometry, a self-similar structure results from the repetition of a design or motif (or “generator”), on a series of different size scales. This repetition of a pattern into different size scales is referred to herein as recursively generated patterns.
Experimentation with non-Euclidean structures has been undertaken with respect to electro-magnetic waves, including radio antennas. Prior art spiral antennas, cone antennas, and V-shaped antennas may be considered as a continuous, deterministic first order fractal, whose motif continuously expands as distance increases from a central point. Unintentionally, first order fractals have been used to distort the shape of dipole and vertical antennas to increase gain, the shapes being defined as a Brownian-type of chaotic fractals. First order fractals have also been used to reduce horn-type antenna geometry, in which a double-ridge horn configuration is used to decrease resonant frequency. The use of rectangular, box-like, and triangular shapes as impedance-matching loading elements to shorten antenna element dimensions is also known in the art.
Whether intentional or not, such prior art attempts to use a quasi-fractal or fractal motif in an antenna employ at best a first order iteration fractal. By first iteration it is meant that one Euclidian structure is loaded with another Euclidean structure in a repetitive fashion, using the same size for repetition.
Antennas designed with fractal generators and a number of iterations, which is referred to herein as fractal geometry, appear to offer performance advantages over the conventional Euclidian antenna designs. Alternately, even if performance is not improved, the fractal designs permit antennas to be designed in a new form factor. However, the form factor of a fractal antenna need not necessarily be smaller than a comparable Euclidian antenna, and it need not fit within the constraints of a portable wireless communication device package.
More critically, a fractal geometry antenna has limitations with respect to the resonating frequency bands. Fractal pattern iterations have a precise mathematical relationship. As a result, the resonating frequencies of a fractal antenna have a predetermined spacing between resonances. For example, the fundamental antenna structure may resonate at cellular band frequencies of 824 to 894 megahertz (MHz). The first fractal pattern iteration of such an antenna would create structures that resonant at 1648 to 1788 MHz (twice the initial frequency). This higher frequency band is of little use if the antenna is expected to operate in the cellular band and either the PCS band (1850 to 1990 MHz), or the global positioning satellite (GPS) band at 1565 to 1585 MHz.
It would be advantageous if some of the general concepts of fractal geometry antennas could be used to build an antenna that resonated at frequency bands non-proportionately related.